1. Field of the Invention
The present invention relates to a vacuum apparatus including a vacuum pump having at least one stage, and a high vacuum junction and a fore vacuum junction arranged on opposite sides of the at least one stage, with gas flowing from the high vacuum junction to the fore vacuum junction, and a method of controlling the suction speed of the vacuum pump.
2. Description of the Prior Art
In apparatuses used for effecting vacuum processes, e.g., chemical processes or processes used in manufacturing of semi-conductors, a large conductance should be available between a vacuum chamber, in which a process is effected, and a vacuum pump which adjoins the vacuum chamber, to provide for rapid pumping-out of gaseous by-products. On the other hand, the adjustment and maintenance of a predetermined pressure of a gas or a gas mixture, at which the process is conducted, requires a definite and reproducible suction speed of the vacuum pump.
In conventional apparatuses, control valves, which are provided between the vacuum chamber and the vacuum pump, are used for controlling the suction speed of the vacuum pump. Because of the required large conductance, the control valves usually have large diameters. This leads to an expensive construction with high costs of manufacturing and also to a large volumetric expansion of its elements. In addition, these control valves need to meet particular requirements, resulting from their use in the high vacuum region.
Another possibility of controlling the suction speed at the high vacuum side becomes available when rotary vacuum pumps are used for pumping gas out of a vacuum chamber. In these pumps, the suction speed can be controlled by controlling the rotational speed of the rotary vacuum pump. The drawback of this solution consists in that the control is relatively slow and does not adequately respond to changes of the pressure in the vacuum chamber
Further, the control of the suction speed at the high vacuum side should be coordinated with a corresponding control of the fore vacuum pressure which should be effected in a simple manner. The necessity to coordinate the control of the suction speed at the high vacuum side with the control of the fore vacuum fore vacuum pressure makes the achievement of a definite reproducible adjustment of the required relationships at the high vacuum side difficult because the control of the suction speed should be very steep, i.e., small adjustments at the fore vacuum side require big changes at the high vacuum side. Besides, because of a high pressure at the fore vacuum side, condensation and, in case of use of aggressive process gases, corrosion, which occur in the control valves, limit their use.
Accordingly, an object of the present invention is to provide a vacuum apparatus and a method of controlling its suction speed which would eliminate the drawbacks of the prior art apparatuses and methods.
Another object of the present invention is to provide a vacuum apparatus and a method which would insure a simple and reproducible adjustment of the suction speed and would permit to adapt the suction speed to requirements of a particular vacuum process.
A further object of the present invention is to provide an apparatus having inexpensive construction and in which condensation and corrosion are prevented.